A liquid crystal display device controls the light transmissivity of liquid crystal by use of electric field, thereby displaying a picture. The liquid crystal display device, as shown in FIG. 1, includes a thin film transistor substrate 70 and a color filter substrate 80 which face each other to be bonded together with a liquid crystal 76 therebetween.
In the color filter substrate 80, a color filter array including a black matrix 68 for preventing light leakage, a color filter 62 for realizing color, a common electrode 64 forming a vertical electric field with a pixel electrode 72, and an upper alignment film (not shown) which is spread thereover for aligning the liquid crystal is formed on an upper substrate 11.
In the thin film transistor substrate 70, a thin film transistor array including a gate line 82 and a data line 74 formed to cross each other, a thin film transistor 58 formed at an intersection thereof 82, 74, a pixel electrode 72 connected to the thin film transistor 58, a lower alignment film spread thereover for aligning the liquid crystal is formed on a lower substrate 21. Also, the thin film transistor substrate further includes a gate pad 78 extended from the gate line 82 and a data pad 66 extended from the data line 74.
The liquid crystal display device has the common electrode formed on the upper substrate 80 and the pixel electrode formed on the lower substrate 70 arranged to face each other, and drives the liquid crystal 76 of twisted nematic TN mode by the vertical electric field which is formed therebetween. The vertical electric field type liquid crystal display has an advantage in that its aperture ratio is high, but a disadvantage in that its viewing angle is narrow to be about 90 degree.
Accordingly, there has recently been proposed a horizontal electric field type liquid crystal display device having a wide viewing angle of about 160 degree by driving a liquid crystal of in-plane switching (IPS) mode by a horizontal electric field between the pixel electrode and the common electrode which are arranged in parallel on the lower substrate.
In the IPS mode liquid crystal display device, the thin film transistor substrate includes a semiconductor process and requires a plurality of mask processes, thus its fabricating process become complicated to be a main factor of the cost increase in fabricating the liquid crystal display panel. In order to solve this problem, the thin film transistor substrate has been developing in a direction of reducing the number of mask processes. This is because one mask process includes many sub-processes such as a thin film deposition process, a cleaning process, a photolithography process, an etching process, a photo-resist peeling process, an inspection process and so on. Accordingly, there is recently required a thin film transistor substrate and a fabricating method thereof that might be able to reduce the fabricating cost by reducing the fabricating process of the thin film transistor substrate.